The present invention relates to an intake control apparatus and method for an internal combustion engine, which is configured to control an intake air amount by variable control of a lift and operation angle of an intake valve, and particularly to a technique for learning a controlled position of a variable valve operating mechanism for variable control of the lift and operation angle of the intake valve. The present invention further relates to an intake control apparatus and method for controlling an idle speed of an internal combustion engine.
In a gasoline engine, an intake air amount is generally controlled by a throttle valve disposed in an intake passage. However, as is well known, such an intake control encounters a problem that there is caused a large pumping loss particularly under middle to low load conditions where the opening degree of the throttle valve is small. To solve such a problem, it has been tried to develop a technique of controlling the intake air amount without depending upon the throttle valve and it has been proposed, by using such a technique, to realize an arrangement in which an intake system is not provided with a throttle valve similarly to a diesel engine, i.e., a so-called throttle-less arrangement.
In Unexamined Japanese Patent Publications Nos. 2002-256905 and 2003-74318, which are assigned to the same assignee of this application, is disclosed a variable valve operating device consisting of a first variable valve operating mechanism capable of varying a lift and operation angle simultaneously and continuously and a second variable valve operating mechanism capable of varying a maximum lift phase (i.e., a phase at which the lift becomes maximum). By such a variable valve operating device, an amount of intake air to b e supplied to cylinders can be controlled independently of the opening degree of the throttle valve, and particularly under a low load condition a so-called throttle-less operation or an operation where the opening degree of the throttle valve is kept sufficiently large can be realized, thus reducing a pumping loss considerably. Further, by controlling so that a valve lift amount is so small at idle, the intake air amount can be controlled accurately.
In the meantime, in an arrangement of controlling the intake air amount by variable control of the valve lift characteristics, a vacuum is not produced in the intake system if the arrangement is of the completely throttle-less type, i.e., of the type not provided with a throttle valve. This causes a new problem that conventional systems such as a system for circulating blow-by gas or purge gas from an evaporator can not be used or a vacuum that is used as a drive source for various actuators cannot be obtained. To solve such a problem, it has been proposed to dispose a so-called electronically controlled throttle valve as a vacuum control valve in an intake passage to realize, in combination with an opening degree control of the throttle valve, a control of an intake air amount through control of the valve lift characteristics of the intake valve while obtaining a predetermined vacuum in the intake passage.
Further, in Unexamined Japanese Patent Publication No. 11-36896 corresponding to U.S. Pat. No. 6,039,026 is disclosed such a technique as follows. Namely, in an arrangement for controlling an amount of intake air to be supplied to an internal combustion engine by using a throttle valve, a fully closed position of a throttle valve is controlled mechanically by using a stopper mechanism. An opening degree of the throttle valve detected by an throttle position sensor when the throttle valve is positioned at such a controlled position is learned as a fully closed position with a view to improving the accuracy in control of the throttle valve.
Further, in an automotive gasoline engine, as is well known, an intake air amount at idle is adjusted based on an actual engine speed by controlling an opening degree of an idle control valve disposed in a secondary air passage that bypasses the throttle valve and a feedback control is performed so that the engine speed is held at a target idle speed. It is also known that on the basis of a feedback control value during the feedback control, an intake air amount at idle for obtaining the target idle speed (e.g., an opening degree correction value of the idle control valve) is learned to perform a control by using a learned value with a view to improving the responsiveness of the feedback control and the accuracy of the open-loop control.
Unexamined Japanese Patent Publication No. 11-93736 discloses a similar idle speed control that is realized by controlling an opening degree of an electronically controlled throttle valve.